Reflector assembly for reflecting the vapors of high temperature volatile materials

ABSTRACT

A vapor reflector assembly disposed in a vapor deposition chamber comprises a thin, fluorinated resin film coated onto a support body and means to heat said film to an elevated temperature.

United States Patent Murakami et a1.

[54] REFLECTOR ASSEMBLY FOR REFLECTING THE VAPORS OF HIGH TEMPERATUREVOLATILE MATERIALS Yoshio Murakami; Takasi Yamazaki, both of Yokohama,Japan Tokyo Shibaura Kawasaki-shi, Japan Feb. 8, 1971 Inventors:

[73] Assignee: Electric Co., Ltd.,

Filed:

Appl. No.:

[30] Foreign Application Priority Data References Cited UNITED STATESPATENTS 7/1940 Ledcrer ..118/49 X [451 July 25,1972

2,640,904 6/1953 Gaiser 219/203 X 2,892,263 6/1959 l-Iornbostel 34/DIG.3 2,983,816 5/1961 Koller 117/211 X 3,282,249 1l/1966 Ramsay ..118/6203,287,684 11/1966 Armbruster, Jr ..219/543 X 3,288,638 11/1966 VanPaassen et al.. ....118/49.1 X 3,361,591 1/1968 Dill et a1. ....118/49.1X 3,495,259 2/1970 Rocholl et a1... ..219/522 3,395,674 8/1968 Burham eta1. ..118/49.1 3,358,438 1/1971 Schoenbeck ..203/86 X OTHER PUBLICATIONSIBM Technical Disclosure Bulletin, Vacuum Evaporator With ReevaporationFilament Hornbeck et al., Vol. 12, No. 12, (May 1970) pg. 2083 NewProduct Technical Bulletin-Fabrics and Finishes Dept.-Chemical Div.,Teflon-Coated Glass Fabrics, Tapes and Laminates," Bulletin No. 3,(March 1, 1950) E. I. du Pont de Nemours & Co., (inc) pp. 1- 4 PrimaryExaminer-Morris Kaplan Anorne v--Kemon, Palmer & Estabrook [57] ABSTRACTA vapor reflector assembly disposed in a vapor deposition chambercomprises a thin, fluorinated resin film coated onto a support body andmeans to heat said film to an elevated temperature.

12 Claims, 14 Drawing Figures Patented July 25, 1972 3,678,889

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F l G. 7 (b) INVENTOR.

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\ II'Iliilll I K/ m? T m 4 4 W M wm Mw V/ BACKGROUND OF THE INVENTIONThe present invention relates to a reflector assembly for reflecting thevapors of high temperature volatile materials which consists inreflecting substantially all said vapors in any desired directionwithout their deposition.

The term high temperature volatile materials, as used in the presentinvention, is defined to mean those materials which have a low vaporpressure at normal temperature and can not be quickly vaporized unlessheated to high temperatures.

In an apparatus evacuated to treat the aforementioned vapors, forexample, in a vacuum evaporator, if it is possible to change thedirection of atomic or molecular beams, then there will be obtainedconsiderable convenience, enabling vacuum deposition to be utilized inwider fields. Since, however, neutral atoms or molecules only advance ina bee-line in an evacuated space, it is impossible to deflect theirtravelling I course, unless they are ionized in advance by impingementof electrons thereon and the resulting ionized beams are diverted by anelectric or magnetic field. However, creation of high concentratedionized beams is accompanied with great difficulty and moreover requiresexpensive equipment. In this connection, it may be contemplated toreflect neutral atoms or molecules on a solid or liquid surface as ameans of diverting their proceeding course. While it is notfundamentally impossible to use a solid or liquid surface as areflection plane, the temperature of said reflection plane shouldgenerally be maintained at a level approximating the evaporationtemperature of a material whose vapors are to be diverted by saidreflection plane, (as used herein, the evaporation temperature isdefined to mean that at which the vapor pressure of said material standsat torr). That is, the reflection plane should be considerably heated,for example, to about l,450 C for the vapors of gold and about l,500 Cfor those of nickel. At such high temperatures, there often occurproblems in connection with the vapor pressure and dissociation pressureof a material constituting the reflection plane itself and its reactionwith the vapors of other materials which are to be diverted by saidreflection plane. Since the radiant energy emitted from the reflectionplane grows large in proportion to the fourthpower of the absolutetemperature of the reflection plane, it is often technically difficultto provide a broad reflection plane kept at high temperatures within anevaporation chamber. There are also known other processes of reflectingthe vapors of certain high temperature volatile metals using a greasesurface maintained at approximately normaltemperature. Since, however,these materials are normally in liquid form and have so low a viscosityas to leak out upon exposure to high temperatures most likely tocontaminate the interior of the evaporation chamber and decompose orpolymerize themselves under impingement of high temperature vapors, theyfail to serve as a practical reflector.

Further, the viewing window of a vacuum evaporator or vacuum meltingfurnace is located at a point permitting naked eye observation of asource of vaporizing materials and the molten portion thereof anddirectly receives vapors from said source of molten portion. Thereforethe inside of said window is readily clouded with vapor deposits. Forexample, the viewing window is rendered opaque when there are depositedgold vapors to a thickness of only several hundred A. units. Among theknown devices, therefore, is one wherein the inside of the viewingwindow is fitted with a shutter plate so designed as to be opened onlywhen required. However, this type of device is unadupted for the casewhere there should be continuously performed a close watch. In addition,there has been proposed another device wherein there is used a revolvingdisc provided with a plurality of glass windows in advance, and in caseany of said glass windows is clouded, a fresh clean glass window isbrought to the viewing opening. With this device, however,

the individual glass windows are unavoidably reduced in size, onlypermitting a narrow field of view. As described above, any of thedevices known to date does not originate with a concept of reflectingsubstantially all the vapors of high temperature volatile materials toprevent their deposition.

SUMMARY OF THE INVENTION The present invention has been accomplished inview of the aforementioned situation and is intended to provide areflector assembly for reflecting substantially all the vapors of hightemperature volatile materials in any desired direction in an evacuatedvessel.

Another object of the invention is to provide a reflector assemblywherein a fluorinated resin film for reflecting the vapors of hightemperature volatile materials and a heat element for heating said filmare formed into an integral body.

Still another object of the invention is to provide vacuum evaporators,pipes, viewing windows, etc. in which there is used a reflector assemblyaccording to the invention for reflecting the vapors of high temperaturevolatile materials.

Namely, the present invention provides a reflector assembly forreflecting the vapors of high temperature volatile materials whereinthere is placed in a vacuum chamber a fluorinated resin film, togetherwith a heat element thereof so as to cause substantially all the vaporsof said volatile materials to be reflected in any desired directionwithout their deposition.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a curve diagram showing thesticking coefficient of nickel vapors on the surfaces of variousmaterials;

FIG. 2 is a schematic sectional view of vapor reflecting device asprepared by the present invention;

FIGS. 3, 4 and 5 are schematic sectional views of other embodiments ofvapor reflecting devices as prepared by the present invention;

FIGS. 6 and 7(a) are schematic sectional views of a vacuum evaporatorprovided with a vapor reflecting device of the present invention;

FIG. 7(b) is a partial sectional view of a substrate to be deposited ofa vapor using vacuum evaporator of FIG. 7(a);

FIG. 8 is a sectional view of a pipe for conducting vapors of hightemperature volatile materials provided with a vapor reflecting deviceof the present invention;

FIG. 9 is a schematic view of a vacuum evaporator housing a pipe forconducting vapors of high temperature volatile materials provided with avapor reflecting device of the present invention;

FIG. 10 is a sectional view of the pipe shown in FIG. 9;

FIG. 11 is a sectional side view of a viewing window provided with avapor reflecting device of the present invention;

FIG. 12 is a sectional side view of another embodiment of a viewingwindow according to the present invention; and

FIG. 13 is a plane view of the vapor reflecting device as employed inFIG. 12.

DETAILED DESCRIPTION OF THE INVENTION Thermal evaporation or sputteringof metals, semiconductors and insulation materials in vacuum oftencauses their vapors to condense to form thin films on that part of theinner wall of the vessel facing said materials. Formation of such filmsis generally supposed to arise through the following process. Evaporatedatoms or molecules (hereinafter referred to as the atoms) are adsorbedto the inner surface of the vessel upon their arrival and, after beingretained there for a certain lengthof time, are desorbed. The adsorbedatoms move about over said surface as if in the form of atwo-dimensional gas. In this case, some of the adsorbed atoms arecaptured at point defects on said surface or are formed intoagglomerates consisting of more than one atom due to collision of thesame kind of atoms on each other, thus creating stable nuclei. However,the other portions of said adsorbed atoms which had no chance of growinginto nuclei while being retained on the surface are again evaporated.The average retention time of a single atom on the surface is generallydetermined by the kind of the atom, and the structure, temperature andcondition of said surface. Where said retention lasts only for anextremely short time, there does not occur the condensation of vaporsdue to the lack of a chance of growing into nuclei on the surface forthe above-mentioned reason. For full reflection of vapors, therefore, itis only required to find the conditions in which adsorbed atoms areretained for an extremely short time on average.

From this point of view, the present inventors have repeated a largenumber of experiments. As a result, they have discovered that given thesame kind of adsorbed atom and the same temperature of a vaporreflector, said atom indicates appreciably different average retentiontimes depending on the material of said vapor reflector. It has alsobeen disclosed that above all, materials of fluorinated resin base havea surface which is characterized by unique physical properties in thisrespect, that is, allows atoms adsorbed thereto to be retained for a farshorter period than the surface of any other materials. Among suchfluorinated resin materials, polyfluoroethylenepropylene (hereinafterreferred to as P- FEPI) and polytetrafluoroethylene (hereinafterreferred to as PTFE) are found to be most preferred.

For example, the surface of the aforementioned PFEP or PTFE at 250 Creally prevents the deposition thereto of even high temperature volatilematerials such as silver, gold, nickel, iron, chromium, tungsten andcarbon. It is known that the vapors of low temperature volatilematerials such as cadmium and zinc (cadmium evaporates at about 260 Cand zinc at about 340 C) do not sometimes condense on the surface of,for example, a glass substrate even at about normal temperature. Incontrast, the vapors of high temperature volatile materials such asgold, nickel and iron never fail to be deposited on the surface of amaterial kept at a relatively low temperature, except for the aforesaidgrease surface.

To illustrate the unique physical properties of the surface of i a PTFEor PFEP film, FIG. 1 indicates the sticking coefficient (the density ofincoming atoms taken to be about I atoms/em sec.) of nickel vapor on thesurfaces of polyimide and glass, as plotted according to the temperatureof a substrate. As used herein, the sticking coefficient is expressed interms of the proportions of permanently condensed atoms among thosearriving at a fresh substrate surface on which there does not proceedthe growth of a deposit. Said coefficient is closely related to theaverage retention time of atoms adsorbed on the substrate surface. Theinitial sticking coefficient of nickel vapor on the surface of a PT FEor PFEP film indicates very low values. Particularly when the substratesurface has a temperature of above 200 C, the coefficient on a PTFE orPFEP film is substantially zero, whereas the coefficient on a polyimideresin film or glass plate is approximately unity.

If it is thick enough to preserve a full mechanical strength by itself,a fluorinated resin film may be used singly as a vapor reflector. Thefilm may be indirectly heated by a nichrome heater or infrared ray lamp.Or to efiect uniform distribution of temperature on said film, it ispossible to heat-seal it to a block of metal or ceramic material inwhich there is embedded a heat element. In this case, however, theheating and cooling of said block consumes much time due to its largeheat capacity. It has been experimentally shown that replacement of areflector, if required, after its use of a certain length of timebecomes appreciably troublesome. Accordingly, the reflector may belaminated, as illustrated in FIGS. 2 to 5, with a thin film heat elementso as to ensure a uniform temperature distribution throughout theintegral body.

FIG. 2 represents a laminate reflector assembly prepared'by heat-sealinga film of PFEP (throughout the embodiments of the present inventionthere was used the PFEP material manufactured by du Pont Companycommerically known as Teflon" FEP Type A) on one side of a metal foil 1.The foil 1 consists of, for example, a layer of nickel, nichrome orstainless steel about to 100 microns thick.

FIG. 3 shows a laminate reflector assembly prepared by depositing a thinlayer 21 of tin oxide or other metals on a thin substrate 23 of glass orceramics, leading out electrodes (not shown) from both ends of said massand heat-sealing a PFEP film to the surface of said thin layer 21. Thethin layer 21 of tin oxide or other metals acts as an electricresistance heat element. The layer 21 of tin oxide is formed by sprayingtin chloride on the surface of the substrate heated to about 500 C.Where metals are used in forming said layer 21, nichrome, tantalum orstainless steel is vacuum deposited or sputtered on the substrate 23.The PFEP film 22, 10 to 15 microns thick, is placed on the heat element21 deposited on the substrate 23. The entire mass is heated to 260 to280 C in a vacuum furnace to form a reflector assembly.

FIG. 4 indicates a laminate reflector assembly prepared by mounting aribbon-shaped heat element 31 bent in parallel arrangement illustratedin FIG. 13 on one side of the same kind of substrate 23 as used in FIG.3 and depositing the PFEP film 32 on the opposite side of said substrate23.

FIG. 5 illustrates a laminate reflector assembly prepared by depositingthe PFEP film 42 on both sides of the same kind of metal foil 41 as usedin FIG. 2.

Reflector assemblies shown in FIGS. 2 to 5 can be easily fabricated inany desired size. Since the reflector film is integrally formed with theheat element and directly heated thereby, it permits easy temperaturecontrol. Further the laminate reflector assembly is appreciably reducedin heat capacity offering the advantage of being heated and cooled in ashort time and moreover causing temperature to be uniformly distributedthroughout.

FIGS. 6 and 7(a) respectively represent the cases where the reflectorassembly of the present invention for reflecting the vapors of hightemperature volatile materials is applied in a vacuum evaporator.Referring to FIG. 6, there are provided in an evaporation chamber 51 anevaporation source 52 for thermally evaporating metals placed in acrucible; a substrate 53 having an upward turned surface sensitive tothe light and radiant heat from the evaporation source 52; a shield 54for shutting off the radiant energy and straight advancing vapors fromthe evaporation source 52; a concave PFEP film reflec tor 55 kept at atemperature of 200 to 250 C; a copper plate 58 in which there areembedded a nichrome heater 56 and thermocouple 57 to control thetemperature of the reflector; and a heat shield 59. The evaporationchamber 51 communicates with an exhaust port 60 disposed below.

In the above-mentioned vacuum evaporator, atoms evaporated from theevaporation source 52 are reflected on the PFEP reflector 55. Part ofthe reflected atoms is brought back to the substrate 53 whose depositionplane is turned upward. This arrangement enables evaporated atoms to bedeposited even on such surface as can not be directly exposed to thelight and radiant heat from an evaporation source due to its highsensitivity thereto.

FIG. 7(a) denotes the case where a reflector assembly according toanother embodiment of the present invention is employed in a vacuumevaporator. In this case, the vacuum evaporator comprises an evaporationsource 62 consisting of a tungsten coil packed with metal material to beevaporated; a small substrate 63 having slight irregularities formed onone side as illustrated in FIG. 7(b) and disposed at right angles to thedirection in which the volatilizable metal material is evaporated fromthe evaporation source 62; a cylindrical PFEP vapor reflector 65 sodisposed as to enclose the evaporation source 62 and substrate 63 andkept at a temperature of 200 to 250 C; a cylindrical copper plate 68 inwhich there are embedded a nichrome heater 66 and thermocouple 67 so asto control the temperature of the reflector; and a group of heat shields69. The evaporation chamber 61 communicates with an exhaust port 70 (notshown) disposed below.

In the vacuum evaporator of FIG. 7(a), some portions of metal atomsevaporated from the evaporation source 62 are directly brought to thesurface of the substrate 63, while the other portions are carried tosaid surface slantwise after being once or twice reflected on thecylindrical reflector 65. This permits evaporated atoms to be depositedeven on a side wall (FIG. 7(b)) which would present difficulties in thedeposition of vapors in an ordinary vacuum evaporator.

To this end, there has heretofore been adopted a complicated process of,for example, providing a plurality of evaporation sources and causing asubstrate to rotate. In contrast, an evaporator using the reflectorassembly of the present invention can attain the object very easily.

As apparent from the aforementioned embodiments of the presentinvention, an evaporator having a reflector assembly disposed in theevaporation chamber enables the passage of vapors to be changed in anydirection desired. Accordingly, the relative positions of theevaporation source, substrate and reflector assembly can of course bechanged according to the object. It is also possible to accumulatevapors in a free space or focus them in an arbitrary direction.

The foregoing embodiments relate to the cases where the PFEP filmreflector was kept at a temperature of 200 to 250 C which is below itssoftening point. The PFEP film becomes soft at temperatures of 260 to280 C at which it is reduced in viscosity. The PTFE resin is supposed tohave a softening point of 310 to 330 C. In this range of temperatures,it reversibly turns translucent or transparent from a white opaquecondition. Unless heated to a temperature appreciably in excess of thesoftening point, these PFEP and PTFE resins have the characteristicsthat they are not turned into liquid form like grease or oil. Further,volumes of gases released from them or amounts of product resulting fromtheir decomposition are small from the standpoint of the vacuumtechnique, that is, present no problems with the normal evacuationprocess. If kept at a temperature slightly above the softening point,the PTFE and PFEP films will cause evaporated atoms to be retained for ashorter time than when heated to below the softening point, and reducethe sticking coefficient of evaporated atoms to zero, whereas saidcoefficient does not fall to zero when said films are heated to belowthe softening point. This is supposed to arise from the fact that whenthe PTFE and PFEP films are heated beyond their softening point, themacromolecules of the resin vibrate more vigorously. It is seen,therefore, that heating of the PTFE and PFEP films should notnecessarily be limited to a temperature below their softening point, butthat there are occasions where heating beyond their softening pointrather gives better results.

As far as the present invention is concerned, the reflector film isheated to a relatively low temperature, whether it rises above or fallsbelow its softening point. Accordingly, said heating can be easilycarried out by a very common method using, for example, a nichromeheater or infrared lamp, presenting few heat problems, unlike theconventional case where the reflector is considerably heated.

As mentioned above, the present invention enables the passage of vaporsto be freely changed, realizing evaporation heretofore consideredinfeasible, accurate evaporating operation, improved physical propertiesof vapor deposited materials and increased evaporation efficiency.

FIGS. 8 to 10 relate to the case where the reflector assembly of thepresent invention is employed in a pipe for conducting vapors of hightemperature volatile materials. Referring to FIG. 8, a pipe assembly 72is prepared by coating the PTFE film 74 manufactured by du Pont Companycommercially known as Teflon TFE on the inner wall of a pipe member 73of stainless steel or other materials generally used in vacuum piping,winding a heater 75 in the form of a coil about the outer periphery ofthe pipe member 73 and mounting a heat insulating layer 76 made of, forexample, glass wool on said coil 75. Numerals 77 and 77 denote vacuumflanges fitted to both ends of the pipe assembly 72. The flange 77 isfitted with a counterpart flange 79 with a gasket 78 interposedtherebetween. The counterpart flange 79 is provided with an exhaust port80 and an input terminal 82 for conducting current to an evaporationsource 81 to generate metal vapors. Numeral 83 represents a concavestainless steel reflector for reflecting evaporated metal atoms. Thereflector 83 has a PTFE film 84 coated on its reflection plane and isfixed to the counterpart flange 79 by a fitting metal part (not shown).The other vacuum flange 77' is similarly fitted with a counterpartflange 79 with a gasket 78' disposed therebetween. On the inner wall ofthe counterpart flange 79' is detachably placed by a holder 86 anevaporation substrate made of glass or ceramics.

In the aforementioned pipe assembly 72, the PT F E film 74 is coated,for example, in the following manner. Finely divided PTFE powders aresuspended in a proper liquid to form a suspension solution at about 45percent concentration. Said solution is coated on the inner wall of thepipe member 73 which was thoroughly water washed in advance, thermallydried at a temperature of to 200 C for about 2 hours and further heatedat about 400 C for about 30 minutes to form a film about 1 to 2 microns.

The pipe assembly 72 constructed as described above is evacuated, andcurrent is conducted through a heater 75 to heat the pipe member 73 to200 to 300 C. When the evaporation source 81 is electrically heated,minute amounts of vapors released from the evaporation source 81 arescattered in all directions as indicated by the arrows A. Since theinner wall of the pipe member 73 is coated with the PTFE film and keptat a temperature of 200 to 300 C, most or all evaporated atoms impingingon said inner wall are reflected for the aforementioned reason.Eventually, most evaporated atoms are deposited on the surface of thesubstrate 85.

Referring to FIG. 9, a pipe assembly 87 using a PTFE or PFEP filmreflector according to the present invention is curvedly disposed in avacuum chamber 88. One end of the pipe assembly 87 opens to anevaporation source 89 and the other end to a target 90. The pipeassembly 87 consists of two hard glass pipe components 91 and 91' shapedin a semicircular form in section and equally split lengthwise. Theinner wall of a pipe member 72 constituted by a combination of said pipecomponents 91 and 91' is coated with a PFEP film 93. The outer peripheryof the pipe member 92 is wound with a nichrome heater 94, which in turnis covered with a heat shield 95. In this case, the PFEP film can be setin place by heat-sealing or depositing raw PFEP on the inner wall of thehard glass pipe components 91 and 91'. In this case, the pipe components91 and 91' are made to abut against each other after the PFEP film isformed and thereafter sealed together in airtight relationship by propermeans.

The aforementioned arrangement enables substantially all vapors releasedfrom the evaporation source 89 to arrive at the target 90, reducing lossof the raw material to be evaporated and in consequence ofleringeconomic advantages. Moreover, the somewhat elongate pipe assembly 87permits an evaporated layer to be formed with a uniform thickness on thetarget 90.

FIGS. 11 and 12 relate to the case where the reflector assembly of thepresent invention is applied in a viewing window. Referring to FIG. 11,there is fitted a viewing glass member 99 by means of a cover ring 98 tothe end of a cylindrical viewing port 97 projecting from the casing 96of an evaporator or vacuum melting furnace. In the cylindrical viewingport 97 is fixed a quartz glass cylinder 100 concentrically therewith bysupport members 101 and 102. In the cylinder 100 is disposed a glassdisc 104, 100 microns thick, coated with a PFEP film 103, 12 micronsthick. The outer periphery of the cylinder 100 is fitted with a heater105 and reflection plate 106. Referring to FIG. 11, numeral 107 denotesa water cooling pipe wound about the cylindrical member 97, 108 an Oring fitted between the viewing glass disc 99 and said cylindricalmember 97, and 109 a ring for holding another glass disc 104.

According to the aforementioned arrangement, while an evaporator orvacuum melting furnace is in operation, the heater 105 is energized toheat the glass disc 104 disposed in the quartz glass cylinder 100 to atemperature of 200 to 250 C. Since atoms adsorbed to the PFEP film 103coated in the inner side of the glass disc 104 are retained for anextremely short time, the formation of nuclei is obstructed to preventthe deposition of evaporated atoms on the surface of the glass disc I04,thereby keeping it clean and transparent over a long period. The viewingglass member 99 is shut off from evaporated materials by the glass disc104, naturally preventing their deposition thereon and serving as aviewing window for a long time. If there is no need to keep a continuouswatch on the interior condition of the evaporator or vacuum meltingfurnace, there may be provided a shutter like that used in the pastbetween the glass disc 104 and said evaporator or melting furnace. Inany case, application of a PT FE or PFEP film reflector assemblyaccording to the present invention enables a viewing glass plate to beused in a satisfactory condition x more than times longer than that ofthe prior art.

FIG. 12 represents the case where the reflector of the present inventionis used in a high vacuum or ultra-high vacuum evaporator. In this case,a viewing glass member 110 is directly sealed to a cylindrical member111 made of Kovar. In the cylindrical member 111 is received a glassdisc 114, the inner side of which is coated with PFEP resin about 1,000A. thick and the other side of which is coated with a transparentconductor film circuit formed of, for example, SnO and arranged in azigzag form illustrated in FIG. 13. The conductor film circuit 113 isenergized by current conducted across the electrodes 115. While theaforesaid evaporator or melting furnace is in operation, the PFEP film112 is electrically heated to a temperature of about 250 C. Said film isextremely transparent, having substantially the same permeability toinfrared rays and visible light as optical glass. When touched byevaporated materials under the aforementioned heated condition, the PFEPfilm substantially prevents them from being deposited thereon.Application of the viewing window of FIG. I2 using the PFEP filmreflector of the present invention in a vacuum evaporator of nickelproved that such viewing window could be used satisfactorily about 50times longer than the conventional type. Further, direct attachment ofthe PFEP film to a viewing glass plate placed in a cylindrical viewingmember gives the same result.

What we claim is:

I. In apparatus for handling vapors of high temperature volatilematerial under reduced pressure to deposit a layer of said material upona substrate comprising a vacuum chamber and means to position assubstrate therein for deposition of said layer, the improvement whichcomprises a reflector assembly for reflecting said vapors of hightemperature volatile material positioned within said vacuum chamber,said assembly comprising a thin fluorinated resin film coated on asupport surface and heating means to heat said film to an elevatedtemperature.

2. The reflector assembly according to claim 1 wherein the fluorinatedresin is either of polytetrafluoroethylene andpolyfluoroethylenepropylene.

3. The reflector assembly according to claim 1 wherein the heat elementis disposed on the opposite side of the reflecting plane of thefluorinated resin film.

4. The reflector assembly according to claim3 wherein the heat elementis fabricated in sheet form and directly disposed on the opposite sideof the reflecting plane of the fluorinated resin film.

5. The reflector assembly according to claim 4 wherein the heat elementis one selected from the group consisting of tin oxide, nichrome,nickel, tantalum and stainless steel.

6. The reflector assembly according to claim 5 wherein the metalconstituting the heat element is mounted on a non-conductive substratein the form of a thin film.

7. The reflector assembly according to claim 6 wherein thenon-conductive substrate is either of glass and ceramics.

8. The reflector assembly according to claim 3 wherein the heat elementmounted on one side of the non-conductive substrate assumes a ribbonshape bent in parallel arrangement and the reflector is disposed on theopposite side of said substrate.

9. In apparatus for handling vapors of high temperature volatilematerial under reduced pressure to deposit a layer of said material upona substrate comprising a vacuum chamber and means to position asubstrate therein for deposition of said layer, the improvement whichcomprises a viewing window for said chamber, said window comprising atransparent member as the body of said window having an inside surfaceand an outside surface and a reflector assembly positioned adjacent saidinside surface, said reflector assembly comprising a thin, fluorinatedresin film coated onto a transparent body and heating means to heat saidfilm to an elevated temperature at which said film is transparent.

10. A viewing window assembly for apparatus for handling vapors of hightemperature volatile material under reduced pressure to deposit a layerof said material upon a substrate which comprises a plate of transparentmaterial constituting the viewing window, said plate being fitted to andsealing an opening in said apparatus presenting an inside surface acrosssaid opening and a reflector assembly positioned adjacent said insidesurface, said reflector assembly comprising a thin, fluorinated resinfilm coating on a transparent body which is substantially parallel tosaid inside surface and heating means to heat said film to an elevatedtemperature at which said film is transparent.

11. In vacuum deposition apparatus comprising a vacuum chamber, anopening in said vacuum chamber and a viewing window fitted to andsealing said opening, the improvement which comprises a reflectorassembly to mitigate deposition of vapors of high temperature volatilematerials existing in said chamber upon the inner surface of saidwindow, said reflector assembly comprising a thin, fluorinated resinfilm coated onto a transparent body positioned adjacent said innersurface substantially parallel thereto and heating means to heat saidfilm to an elevated temperature at which said film is transparent.

12. A viewing window assembly in vacuum deposition apparatus comprisinga tubular member extending from said apparatus and communicating with avacuum chamber forming part of said apparatus, a plate of transparentmaterial fitted across the outer end of said tubular member forming aseal for said tubular member through which said vacuum chamber may beviewed from without said apparatus, a reflector assembly positionedwithin said tubular member between said plate and said vacuum chamber,said reflector assembly comprising a glass plate, a thin film offluorinated resin coated upon the surface of said glass plate oppositeto said plate of transparent material and on the opposite side of saidglass plate a transparent film of electrically conductive materialconstituting a heating element for said reflector assembly and elecuodesconnected to said transparent film by which to energize said film withcurrent to heat the reflector assembly to an elevated temperature atwhich said film of fluorinated resin is transparent.

l i I! l

1. In apparatus for handling vapors of high temperature volatilematerial under reduced pressure to deposit a layer of said material upona substrate comprising a vacuum chamber and means to position assubstrate therein for deposition of said layer, the improvement whichcomprises a reflector assembly for reflecting said vapors of hightemperature volatile material positioned within said vacuum chamber,said assembly comprising a thin fluorinated resin film coated on asupport surface and heating means to heat said film to an elevatedtemperature.
 2. The reflector assembly according to claim 1 wherein thefluorinated resin is either of polytetrafluoroethylene andpolyfluoroethylenepropylene.
 3. The reflector assembly according toclaim 1 wherein the heat element is disposed on the opposite side of thereflecting plane of the fluorinated resin film.
 4. The reflectorassembly according to claim 3 wherein the heat element is fabricated insheet form and directly disposed on the opposite side of the reflectingplane of the fluorinated resin film.
 5. The reflector assembly accordingto claim 4 wherein the heat element is one selected from the groupconsisting of tin oxide, nichrome, nickel, tantalum and stainless steel.6. The reflector assembly according to claim 5 wherein the metalconstituting the heat element is mounted on a non-conductive substratein the form of a thin film.
 7. The reflector assembly according to claim6 wherein the non-conductive substrate is either of glass and ceramics.8. The reflector assembly according to claim 3 wherein the heat elementmounted on one side of the non-conductive substrate assumes a ribbonshape bent in parallel arrangement and the reflector is disposed on theopposite side of said substrate.
 9. In apparatus for handling vapors ofhigh temperature volatile material under reduced pressure to deposit alayer of said material upon a substrate comprising a vacuum chamber andmeans to position a substrate therein for deposition of said layer, theimprovement which comprises a viewiNg window for said chamber, saidwindow comprising a transparent member as the body of said window havingan inside surface and an outside surface and a reflector assemblypositioned adjacent said inside surface, said reflector assemblycomprising a thin, fluorinated resin film coated onto a transparent bodyand heating means to heat said film to an elevated temperature at whichsaid film is transparent.
 10. A viewing window assembly for apparatusfor handling vapors of high temperature volatile material under reducedpressure to deposit a layer of said material upon a substrate whichcomprises a plate of transparent material constituting the viewingwindow, said plate being fitted to and sealing an opening in saidapparatus presenting an inside surface across said opening and areflector assembly positioned adjacent said inside surface, saidreflector assembly comprising a thin, fluorinated resin film coating ona transparent body which is substantially parallel to said insidesurface and heating means to heat said film to an elevated temperatureat which said film is transparent.
 11. In vacuum deposition apparatuscomprising a vacuum chamber, an opening in said vacuum chamber and aviewing window fitted to and sealing said opening, the improvement whichcomprises a reflector assembly to mitigate deposition of vapors of hightemperature volatile materials existing in said chamber upon the innersurface of said window, said reflector assembly comprising a thin,fluorinated resin film coated onto a transparent body positionedadjacent said inner surface substantially parallel thereto and heatingmeans to heat said film to an elevated temperature at which said film istransparent.
 12. A viewing window assembly in vacuum depositionapparatus comprising a tubular member extending from said apparatus andcommunicating with a vacuum chamber forming part of said apparatus, aplate of transparent material fitted across the outer end of saidtubular member forming a seal for said tubular member through which saidvacuum chamber may be viewed from without said apparatus, a reflectorassembly positioned within said tubular member between said plate andsaid vacuum chamber, said reflector assembly comprising a glass plate, athin film of fluorinated resin coated upon the surface of said glassplate opposite to said plate of transparent material and on the oppositeside of said glass plate a transparent film of electrically conductivematerial constituting a heating element for said reflector assembly andelectrodes connected to said transparent film by which to energize saidfilm with current to heat the reflector assembly to an elevatedtemperature at which said film of fluorinated resin is transparent.